Thermal plug cut-out



July 17, 1928.

M. J. SANDIN THERMAL PLUG CUTOUT Filed Jan. 23, 1923 INVENTOR Maupi fs J. andln.

A'fTORNEY raj Fig. 2.

WITNESSES:

Patented my 1 7, 1928.

UNITED STATES PATENT OFFICE.

HAURITS J. SANDIN, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTIRIC & MANUFACTURING COMPANY. A CORPORATION OF PENNSYL- vangn.

THERMAL I LUG CUT-OUT.

Application filed January 28, 1928. Serial No. "4,879.

7 My invention relates to electric cutouts and particularly to cutouts of the screw type adapted to be inserted in a standard screw socket for interrupting the circuit under severe overload and short-circuit conditions.

Motors and certain other electrical apparatus may be operated for certain time intervals under overload conditions without becoming seriously overheated. However, when overload conditions prevail for an excessive length of time, the motors or apparatus become heated to a destructive degree;

It is an object of my invention to provide a cutout thatwillinterrupt the circuit after an overload has prevailed a predetermined length of time, the time, of course, being less than that required to injure the motor or apparatus, and to interrupt the circuit immediately upon short-circuit conditions in the circuit.

Another object of my invention is to provide a cutout device wherein an element is responsive to abnormal currents for opening the circuit and which may be readily renewed.

Another object of my invention is to rovide a cutout device, having the above 0 aracteristics, wherein the thermal-responsive element constitutes a refill which may readily be removed after circuit-interrupting operations and which is relatively inexpensive to manufacture and may replaced at small cost.

Another object of my'invention is toprovide a refill which is a, composite unitary structure comprising a heating conductor and an enlarged contact member that are joined by solder in such manner that the solder will be fused upon overload or shortcircuit conditions and permit separation of the terminals that are connected by the refill.

Another object of my invention is to provide a cutout device wherein relatively movable terminals are connected by a thermalresponsive refill and wherein means are provided for separating the terminals when the v solder holding the parts of the refill together has become fused, thereby drawing out the arc and extinguishing it under overload conditions.

Another object of my invention is to provide a thermal cutout that shall be effective for interrupting the circuit under short-circu1t conditions as well as overload conditions, and in which the thermal-responsive element shall be of such character that it will be instantly volatilized when the circuit 1s short-circuited and thereby cause instantaneous interruption of the circuit.

Another object of my invention is to pro vide a cutout device wherein the operative parts of the device are protected from the heated gases incident to the rupture of the thermal-responsive element.

Another object of my invention is to provide a thermal-responsive device wherein one of the terminals serves to close one end of the casing of the device and to constitute a heat-conducting and radiating member for absorbing heat from the thermal-responsive element and to thereby increase the time interval before interruption of the circuit occurs under overload conditions.

A further object of my invention is to provide a cutout device of the above-indicated character wherein refills having differ- .ent heating characteristics may be inserted whereby the same cutout device may be used in circuit with motors or apparatus having different heating characteristicsby simply changing the thermal-responsive refill.

These and other objects, that will be made apparent throughout the further description of my invention, are attained by means of theapparatus hereinafter described, and illustrated in the accompanying drawings, wherein:

Figure 1 is a longitudinal sectional view of the cutout device taken on the line I-I of Fig. 2;

Fig. 2 is an end view of the cutout device with the cover removed, and

Fig. 3 is an elevational view of the cutout device.

Referrin to the drawings, the device includes a tu ular casing 3 that is preferably made of insulating material, such as porcelain or molded insulating compound. The end of the casing is closed at one end and is provided with two longitudinal bores 4 and 5 of diflerent diameters, the latter being the sions 12 and 13 which extend into the large bore of the casing-through an opening 14 therein;

The extension 12 is flexibl connected to a terminal disc 15 by an annu r strip of conductive metal 16 that is riveted, at one end, to the extension 12 and, at the other end, to the disc 15. By reason of the flexible connection, the disc 15 may be repeatedly moved toward the outer end of the bore 5 when the circuit is interrupted without danger of breaking the connection between the disc and the extension 12. The extension 13 serves as a stop for limiting the outward movement of the disc 15.

The disc 15 is provided with a central perforation 17 for receiving the shank of a refill 18 which serves to releasably conductively connect the terminal disc 15 to the terminal sleeve 6.

The thermal-responsive refill 18 comprises a heating conductor 19 that is preferably made of a metal having relatively high resistance and which becomes heated under abnormal current conditions in the circuit in which the conductor is connected. A contact disc 21, having a perforation 22, is connected to the end of the heating conductor 19 by means of a solder 23 that is fusible at a relatively low temperature. As indicated in Fig. .1, the shank 19 of the refill is inserted through the terminal disc 15 and extends into the bore of the'terminal sleeve 6 where it is clamped in position by a set' screw 24.

The terminal disc 15 is normally biased outwardl by means of an insulating tube 25 that ts within the small bore 4 of the casing 3 and is adapted to be moved outwardly by a helical spring 26 disposed between its inner end and the end of the casing. The spring 26 is mounted within a metal s ider member 27 that is attached to a central y disposed sleeve 28 which supports and centers an inner insulating tube 29. The tube 29 telescopes within the. tube 25 and serves as a support for the terminal disc 15 to limit the inward movement thereof.

So long as the thermal-responsive element 18 remains intact, current will flow through the cutout device from the central contact of a receptacle (not shown) which is engaged by the terminal 6. When the plug is in assembled relation within a standard receptacle, current flows from the terminal 6 terminal 9 which is in conductive engagement with the threaded socket of the cutout receptacle (not shown).

When an overload condition is imposed on the circuit for a predetermined time, the.

temperature of the heating conductor 19 rises to the point wherein the solder is heated to its fusing temperature, regardless of the heat that is being conducted away from the contact member 21 by the terminal disc 15. At this time, the solder is fused, and the contact disc 21 and heating conductor 19 are released. Thespring 26 instantly thereafter -moves the terminal disc 15 into engagement with the end of the extension 13 with a snap action, thereb separating the contact disc 21 from the eating conductor 19 in such manner that the arc is instantly extinguished causing interruption of the circuit under an overload condition that avould eventually cause injury to the motor or the apparatus connected in the circuit.

If a short-circuit occurs the heating conductor 19 will instantly be volatilize'd and interrupt the circuit before injury is done to the motor or apparatus connected to the cutout.

In order that the cutout device may be repeatedly used by replacing the thermalresponsive refill, it is necessary to protect the operating parts and terminals from the heated are gases incident to the interruption of the circuit. The terminal disc 15 is, therefore, made of such diameter that it substantially closes the large bore 5, thereby preventing the passage of arc gases past the periphery thereof to the passage 14. The telescoping tubes 25 and 29 prevent the passage of gases to the spring 26. I

As a further precaution against the passage of gases to the spring 26, a washer 31, which snugly fits over the tube 29 and within the bore 4 of the casing, is disposed between the spring and the inner end of the barrier tube 25. It will be seen from the foregoing that, regardless of the position of the movable barrier tube 25 with respect to the tube 29, gases are prevented from entering the space within which the spring 26 is mounted. The cutout device may, consequently, be used repeatedly without injury.

The open end of the receptacle is closed by means of a. detachable cover 32 having an opening 33 therein that is closed by a sheet of transparent mica 34. The outer wall of the casing is provided with depressions 35 which provide shoulders 36 that are adapted to be'engaged by indentations 37 in the flange 38 of the cover 32. Slots 39, leading from the outer face of the end of the receptacle, permit the indentations 37 to pass to the depressions 35 when the cover is moved toward the closed end of the receptacle.

After the indentations 37 have cleared the groove 39, the cover is rotated with respect to the casing, thereby permitting the indentations 37 of the cover to engage the inclined shoulders 36. The cover may be detached by a reverse movement thereof with respect to the casing. By reason of the transparent closure 34, the terminal disc 21 is made visible when it is moved into its outermost position and visibly indicates circuitinterrupting operation of the cutout device.

While I have illustrated and described but one embodiment of my invention, it will be apparent to those skilled in the art that various changes, modifications, substitutions, additions and omissions may be made therein without departing from the spirit and scope of my invention, as set forth in the appended claims.

I claim as my invention:

1. A cutout for electric circuits comprising a pair of terminal members, and a composite renewable thermal-responsive connector comprising a metal conductor disc for conductively and releasably engaging one of the terminal members and a conductor of relatively high-resistance metal joined thereto by a metal fusible at a relatively low temperature releasably and conductively connected to the other terminal.

2. A cutout for electric circuits comprising a cylindrical receptacle closed at one end, a terminal member extending through the closed end of the receptacle having means for detachabl receiving a cutout refill, a terminal mem er adjacent the open end of the receptacle and substantially closin the interior of the receptacle, a thermally-responsive refill for releasably connecting the said terminal members, means for separating the terminals in response to circuit-interruptin operation of the refill and a cylindrical barrier telescoping within the cylinder and movable with the terminal for protecting the terminal separating means from are gases incident to the interruption of the circuit by the thermal-responsive refill.

3. A cutout for electric circuits comprising a tubular receptacle, relatively movable terminals vvithin the receptacle, a movable tubular barrier telescoping Within the receptacle and closed at one end by one of the terminals, a thermal-responsive element releasably connecting the terminals in operative relation, means for moving the barrier for separating the terminals in response to interrupting operation of the said element.

4. A cutout for electric circuits comprising a tubular receptacle having one end closed, relatively movable terminal members within the receptacle, a pair of tubular barriers telescoping within the receptacle, one

of which is closed at one end by the end of the receptacle and the other of which. is closed by one of the terminals, a thermalresponsive element for releasably connecting the said terminals and means for moving one of the barriers for separating the said terminal members in re-ponse to circuitinterrupting operation of the said element.

5. A cutout for electric circuits comprising a pair of relatively movable tubular insulating casings telescoping one within the other and each closed at one end, a terminal member carried by each casing, a thermalresponsive element for releasably connecting the said terminal members and means for relatively moving the ca ings in response to circuit-interrupting operation of the said element.

6. A cutout for electric circuits comprising a pair of relatively movable tubular insulating casings telescoping one within the other, a terminal member carried by each casing, a thermal-responsive element for relcasably connecting the said terminal members and means for relatively moving the casings in response to circuit-interrupting operation of the said element.

7. A cutout device for electric circuits comprising a tubular casing closed at one end, a tubular barrier extending longitudinally of the casing and fixed thereto,- a movable tubular barrier telescoping with the first barrier, a second terminal member carried thereby, a thermal-responsive element for releasably connecting the said terminal members and means for moving the movable barrier for separating the terminals in response to circuit-interrupting operation of the said element.

8. A cutout for electric circuits comprising a tubular casing closed at one end, a barrier telescoping within the casing, a terminal member carried upon the barrier, a terminal member mounted on the casing and extending into the casing adjacent the open end thereof, flexible means for conductively connecting the said terminal members, a third terminal member carried by the easing, a thermal-responsive element for releasably connecting the first and third terminal members, and means for moving the barrier and first terminal member in response to circuit-interrupting operation of the barriers.

9. A cutout for electric circuits comprising a tubular casing having bores of different diameters and closed at one end having the smaller bore, a tubular barrier telescoping within the small bore, a terminal disc for closing the outer end of the barrier disposed in the large bore of the casing, a terminal member disposed exteriorly of the casing and flexibly connected to the said disc, a terminal member disposed exteriorly of thecasing and extending into the small bore of the casing, a current-responsive element for releasably connecting the said terminal members and means for moving the barrier for relatively moving the terminals in response to the circuit-interrupting operation of the said element.

10. A cutout for electric circuits comprising a pair of separate terminal members, a heat-conducting and radiating disc flexibly connected to one of the terminal members and adapted to be moved with respect to both terminal members, a thermal-responsive refill for connecting the radiating disc to the unattached terminal member comprising a perforate contact disc for conductively engaging the radiating disc and a heating conductor soldered in the perforation adapted to separate from the contact disc when the heating conductor attains a predetermined tem perature and means for moving the radiating disc with respect to the unattached terminal when the solder joining the contact disc and the heating conductor is fused.

11. A cutout for electric fixtures comprising a tubular casing closed at one end, a perforate movable termlnal disc slidably mounted in the open end of the casing, and constituting a closure for the casing. a thermal-responsive refill comprising a heating conductor adapted to be inserted through the perforation in the terminal disc and an enlarged contact member soldered to the heating conductor and conductively engaging the terminal disc, a terminal member extending into the closed end of the casing, means for detachably connecting the free end of the heating conductor to the said terlarge bore of the casing and flexibly connected to the threaded terminal, a tubular 'barrier fitting within the small bore and telescoping over the first tubular barrier and engaging the said movable disc, a spring for forcing the movable disc toward the open end of the casing, and a thermal-responsive element for detachably connecting the movable disc and the first said terminal adapted to release the movable disc when the said element operates to interrupt the circuit.

In testimony whereof, I have hereunto subscribed my name this 9th day of January, 1923.

MAURITS J. SANDIN 

